Epidemic megalerythema, also called 5th disease, is a contagious viral infection that usually affects children between the ages of 5 and 10. Benign in the majority of cases, it is characterized by a rash on the cheeks and limbs. 

In 20 to 30% of cases, the disease goes unnoticed. In 70% of cases, mild symptoms appear. Rash on the cheeks (as if the child has been slapped in the face) and a rash that is mottled or made up of raised red papules on the legs, arms and trunk are characteristic of the disease. The child may also have a slight fever, complain of a mild headache, and have a runny nose for a few days. In adolescents and adults, the infection can cause joint pain. 

Symptoms appear about 4 to 14 days after infection (called the incubation period) and last about 5 to 10 days. During the incubation period, the child may sometimes complain of muscle pain, chills and stomach aches. 

In some cases, the pimples may reappear temporarily following exposure to the sun, heat, or in case of fever, exertion or emotional stress. 

Epidemic megalerythema manifests itself differently in children with diseases that affect the red blood cells and in children with diseases that weaken the immune system. In them, parvovirus B19 can cause severe anemia. 

In adults, the rash affects the extremities of the limbs with a distribution in “gloves and socks”. The virus can also trigger a moderate fever and headache. 

The disease is transmitted by the cough and postilions of an infected person. Droplets or aerosols released into the air are inhaled (or transmitted through the hands) to the upper airways (nose, mouth, throat). The infection can therefore quickly spread within the same household or school. 

Infection can also spread from mother to fetus during pregnancy. The infection can be dangerous for the fetus if the mother has not been immunized before pregnancy (it is estimated that one in two women is immune). If the pregnant woman contracts the virus for the first time, the risk of it being transmitted to the fetus is low (3%). In case of fetal infection, consequences on the unborn baby are observed in 10% of cases (death in utero, miscarriages, severe anemia). 

As with most viral infections, there is no specific treatment for epidemic megalerythema. The disease goes away on its own in a few days, without leaving any sequelae. 

Treatment is based on relieving symptoms. Nonsteroidal anti-inflammatory drugs (NSAIDs) or paracetamol can be given to children to lower fever, relieve headache and joint pain. Antihistamines may be prescribed for itchy skin. 

To limit the risk of virus transmission:

• wash your hands regularly and after blowing your nose or sneezing. 
  
• regularly clean the surfaces with which the sick child is in contact (toys, dishes, household linen, etc.).
  
• if you are pregnant, avoid contact with the sick child as much as possible. 
  
• avoid taking the infected child to busy public places (public transport, shops, etc.).
  
• use single-use disposable tissues to blow the child’s nose. 
  
• limit the child’s close contact with siblings. 

This viral infection is most often mild. In very rare cases, however, it can cause acute encephalitis (infection of the brain). 

Erythema infectiosum is also dangerous in certain categories of people:

• immunocompromised people: the virus can cause severe anemia for several months. 
  
• people with chronic hematological diseases (diseases that affect blood cells). Again, the virus can cause severe anemia and a drop in white blood cells, the blood cells that fight viruses.
  
• pregnant women who are not immune: the risk of miscarriage increases if the pregnant woman contracts the virus during the first trimester. There is a risk of severe fetal anemia and generalized edema in the event of contamination in the second and third trimesters of pregnancy. The risk of fetal death is estimated between 5 and 9%. 

The presence of symptoms on physical examination is usually sufficient to diagnose epidemic megalerythema. Additional examinations are often requested to confirm a case in a child at risk of complications or having a pregnant woman in his or her close entourage:

• a PCR diagnostic test: this consists of looking for the DNA of the virus in oropharyngeal secretions. 
  
• antibody serology. 

A pregnant woman who has been in contact with a child who has contracted the virus must quickly see a doctor for a blood test to find out if she is immune or not.